1. Field of the Invention
Composite materials having acoustic and vibration damping properties are disclosed. In particular, composite materials that contain a viscoelastic interleaf are useful, for example, in structures found in aircrafts, such as fuselage skins, stringers and frames. Also contemplated are methods of making the composite material and the structures and aircrafts that contain the composite material.
2. Description of the Related Art
Fiber-reinforced polymer matrix composites (PMCs) are high-performance structural materials that are commonly used in applications requiring resistance to aggressive environments, high strength, and/or low weight. Examples of such applications include aircraft components (e.g. tails, wings, fuselages, propellers), boat hulls, and bicycle frames. PMCs may comprise layers of fibers that are bonded together with a matrix material, such as a polymer resin. The fibers reinforce the matrix, bearing the majority of the load supported by the composite, while the matrix bears a minority portion of the load supported by the composite and also transfers load from broken fibers to intact fibers. In this manner, PMCs may support greater loads than either the matrix or fiber may support alone. Furthermore, by tailoring the reinforcing fibers in a particular geometry or orientation, the composite can be efficiently designed to minimize weight and volume.
Numerous processes have been developed for the manufacture of PMCs. Examples may include wet layup, prepregging, and liquid infusion. In wet layup, the reinforcing fiber is wet with the matrix material, placed into a mold cavity, and allowed to harden or cure. This process may be performed in an automated fashion, such as with a chopper gun or a machine that receives dry fiber rolls, runs them through a resin dip bath, and places the wetted fibers in the mold. Alternatively, the resin may be applied manually using brushes.
In prepregging, composite components are fabricated with pre-impregnated woven fabrics or prepregs. The reinforcing fibers are impregnated with the matrix resin in a controlled fashion and frozen in order to inhibit polymerization of the resin. The frozen prepregs are then shipped and stored in the frozen condition until needed. When manufacturing composite parts from prepregs, the prepregs are, thawed to room temperature, cut to size, and placed in the mold cavity. Once in place, the prepregs are vacuum bagged and cured under pressure to achieve the required fiber volume fraction with a minimum of voids.
The use of advanced composite materials has gained wide acceptance over the last few decades because of their high strength-to-weight and stiffness-to-weight ratios. Advanced composite materials show higher stiffness but inferior damping performance and compared with metals and metal-matrix composites. Thus, there is a need for advanced composite materials having an enhanced damping capacity of a composite structural system with little reduction in stiffness and strength.